Museum-Built Device Helping Astronomers Search for Exoplanets

After nearly a decade of development, construction, and testing, the Gemini Planet Imager (GPI) is pointing skyward and collecting light from distant worlds with the help of a special starlight-blocking device, called a coronagraph, built at the American Museum of Natural History.

Young star: This is a Gemini Planet Imager’s first-light image of the light scattered by a disk of dust orbiting the young star HR4796. The narrow ring is thought to be dust from asteroids or comets left behind by planet formation; some scientists have theorized that the sharp edge of the ring is defined by an unseen planet. The image on the left shows normal light, including both the dust ring and the residual light from the central star scattered by turbulence in the Earth’s atmosphere. The image on the right shows only polarized light. Leftover starlight is unpolarized and hence removed from this image. The light from the front edge of the disk is strongly polarized as it scatters towards us.

Processing by Marshall Perrin, Space Telescope Science Institute

Constructed by a core team of researchers from seven institutions, GPI detects infrared (heat) radiation to image faint Jupiter-like planets next to bright stars and to probe their atmospheres. It also can help researchers examine dusty disks around young stars.

At the American Museum of Natural History, scientists led by Curator Rebecca Oppenheimer designed and built GPI’s coronagraph—a starlight suppression system—using a variety of experimental optics.

Moon of Jupiter: Although the Gemini Planet Imager was designed to look at distant planets, it can also observe objects in our solar system. For example, images taken of Jupiter’s moon Europa (right) can allow scientists to map changes in the satellite’s surface composition. The visible albedo visualization based on data from the Galileo Solid State Imaging project (from the U.S. Geological Survey) is on the left.

“The planets we seek to study are more than a million times fainter than the stars they orbit,” Oppenheimer said. “Our work on starlight suppression over the past 15 years has led to the capability to see such planets using novel types of optics and new techniques for controlling light.”

The first observation targets for GPI were previously known planetary systems including the Beta Pictoris system, which is about 63 light years away. GPI obtained the first spectrum, or chemical fingerprint, of the very young planet Beta Pictoris b. The first-light team also used the instrument’s polarization mode, which can detect starlight scattered by tiny particles, to study a faint ring of dust orbiting the very young star HR4796. With previous instruments, only the edges of this dust ring, which may be the debris remaining from planet formation, could be seen. But with GPI, astronomers can follow the entire circumference of the ring.

Giant planet: Gemini Planet Imager’s first-light image of Beta Pictoris b, a planet orbiting the star Beta Pictoris. In addition to the image, GPI obtains a spectrum from every pixel element in the field of view to allow scientists to study the planet in great detail. Beta Pictoris b is a giant planet—several times larger than Jupiter—and is approximately 10 million years old. These near-infrared images show the planet glowing in infrared light from the heat released in its formation. The bright star Beta Pictoris is hidden behind a mask in the center of the image.

Processing by Christian Marois, NRC Canada

The group also observed the system of planets orbiting HR8799, a star about 128 light years away.

Another very similar instrument, Project 1640, led by the American Museum of Natural History, was deployed at Palomar Observatory’s 5-meter Hale Telescope in California last year and has demonstrated the power of these techniques on a smaller telescope in the Northern Hemisphere. The two instruments are complementary, and collaboration will begin with the launch this year of GPI’s large-scale survey, which will look at 600 young stars to see what giant planets orbit them.